1. Field of the Invention
The present invention relates generally to an article transfer apparatus, and more particularly to such an apparatus being provided with a pair of grippers at each of the ends of a rotatable transfer arm for simultaneously gripping and mutually replacing two articles.
2. Description of the Prior Art
Heretofore, as transfer apparatus of the above type, there has been known an apparatus in which power actuators are respectively provided on both ends of a transfer arm. In such apparatus, however, the rotational movement of the transfer arm is apt to allow the grippers to open, whereby the articles will fall therefrom due to the centrifugal force which acts upon the articles during such rotational movement. Additionally, other problems exist, such as the possible operation of the two power actuators with a time difference, and further that operations of the actuators are too difficult to detect.
Another apparatus has also been known in which one power actuator is used to actuate both sets of grippers provided on the ends of the transfer arm. In this apparatus, however, when a difference is present between the diameters of the gripped portions of two articles to be gripped, a tight grip is effected on the larger one while a loose grip is effected on th smaller one. For this reason, it is impossible for the apparatus to reliably hold the articles during the transfer operation.